Method and apparatus for dynamic lithographic exposure

ABSTRACT

The present disclosure, in some embodiments, relates to a photolithography tool. The photolithography tool includes a source configured to generate electromagnetic radiation. A dynamic focal system is configured to provide the electromagnetic radiation to a plurality of different vertical positions over a substrate stage. The plurality of different vertical positions include a first position having a first depth of focus and a second position having a second depth of focus that is below the first depth of focus and that vertically overlaps the first depth of focus.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/850,285, filed on Apr. 16, 2020, which is a Continuation of U.S.application Ser. No. 16/202,530, filed on Nov. 28, 2018 (now U.S. Pat.No. 10,663,868, issued on May 26, 2020), which is a Divisional of U.S.application Ser. No. 15/400,015, filed on Jan. 6, 2017 (now U.S. Pat.No. 10,274,830, issued on Apr. 30, 2019), which claims the benefit ofU.S. Provisional Application No. 62/287,591 filed on Jan. 27, 2016. Thecontents of the above-referenced patent applications are herebyincorporated by reference in their entirety.

BACKGROUND

Integrated chips are fabricated in semiconductor fabrication facilitiesor fabs. Fabs contain processing tools that are configured to performprocessing steps (e.g., etching steps, photolithography steps,deposition steps, etc.) upon a semiconductor substrate (e.g., a siliconwafer). Photolithography is a commonly used fabrication process by whicha photomask having a pattern is irradiated with electromagneticradiation to transfer the pattern onto a photosensitive materialoverlying a substrate. Selective parts of the substrate may besubsequently processed according to the patterned photosensitivematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of amethod of dynamically exposing a photosensitive material over aplurality of depths of focus respectively spanning a different region ofthe photosensitive material.

FIG. 2 illustrates a flow diagram of some embodiments of a method ofdynamically exposing a photosensitive material over a plurality ofdepths of focus respectively spanning a different region of thephotosensitive material.

FIGS. 3-6 illustrate cross-sectional views of some embodiments of amethod of dynamically exposing a photosensitive material over aplurality of depths of focus.

FIGS. 7A-7B illustrate some embodiments of a dynamic lithographicexposure tool configured to expose a photosensitive material over aplurality of depths of focus.

FIG. 8 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool.

FIG. 9 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool.

FIG. 10 illustrates a block diagram of some embodiments of a dynamiclithographic exposure tool for an extreme ultraviolet (EUV) lithographysystem.

FIG. 11 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool for an EUV lithography system.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Over the history of the semiconductor industry, the minimum featuressizes of components within an integrated chip have generally decreased.Smaller minimum features sizes have largely been achieved by improving aresolution of photolithography tools used to print such features.However, as the resolution of a photolithography tool improves the depthof focus of the electromagnetic radiation generated by thephotolithography tool focus decreases. It has been appreciated that asthe depth of focus decreases, a process window of a photolithographytool shrinks. If the exposure of a photoresist layer goes outside of theprocess window of a photolithography tool, sections of the photoresistlayer may not be sufficiently exposed and a corresponding feature maynot be properly printed. This can lead to yield lost and/or integratedchip failure.

The present disclosure relates to a dynamic lithographic exposuremethod, and an associated apparatus, which changes a focus (e.g., alocation of an image plane, a location of a depth of focus, etc.) ofelectromagnetic radiation during exposure of a photosensitive material.Changing the focus of the electromagnetic radiation during the exposurecauses the electromagnetic radiation to have a plurality of differentdepths of focus respectively spanning different regions of thephotosensitive material. The different depths of focus collectivelyexpose the photosensitive material according to a cumulative depth offocus that is larger than the individual different depths of focus, andtherefore results in a larger lithographic process window that improvesexposure of the photosensitive material.

FIG. 1 illustrates some embodiments of a cross-sectional view 100showing a method of dynamically exposing a photosensitive material overa plurality of depths of focus respectively spanning a different regionof the photosensitive material.

As shown in cross-sectional view 100, a photosensitive material 104(e.g., a photoresist) is formed over a substrate 102. The photosensitivematerial 104 is selectively exposed to electromagnetic radiation 108generated by a photolithography tool 116 to modify a solubility of anexposed region and define a soluble region 106 having a patterncorresponding to a photomask 118. During the exposure, theelectromagnetic radiation 108 is dynamically focused along a pluralityof different paths 108 a-108 b respectively corresponding to imageplanes 110 a-110 b (i.e., planes along which an image is projected)located at different vertical positions.

For example, at a first time (t=1) the photolithography tool 116 mayfocus electromagnetic radiation 108 along a first path 108 acorresponding to a first image plane 110 a located at a first depthbelow an upper surface 104 u of the photosensitive material 104. At asubsequent second time (t=2), the photolithography tool 116 may focuselectromagnetic radiation 108 along a second path 108 b corresponding toa second image plane 110 b located at a second depth below the uppersurface 104 u of the photosensitive material 104. In some embodiments,images formed on the first image plane 110 a and the second image plane110 b may be offset in a vertical direction and substantially alignedalong a lateral direction (extending parallel to an upper surface of thephotosensitive material 104). In some embodiments, the photolithographytool 116 may focus the electromagnetic radiation 108 in a manner thatmonotonically increases a depth of an image plane within thephotosensitive material 104 (e.g., so that the depth of the image planegets larger as time progresses).

The plurality of image planes 110 a-110 b have different depths of focus112 a-112 b (i.e., a distance extending in opposite directions from animage plane within which a projected image has acceptable opticalproperties, such as focus, dose, etc., to expose the photosensitivematerial 104). The different depths of focus 112 a-112 c respectivelyspan a different region within the photosensitive material 104. Forexample, the first image plane 110 a has a first depth of focus 112 aextending from the upper surface 104 u of the photosensitive material104 to a first position within the photosensitive material 104. Thesecond image plane 110 b has a second depth of focus 112 b extendingfrom the first position within the photosensitive material 104 to asecond position within the photosensitive material 104.

In some embodiments, the plurality of depths of focus 112 a-112 b maycontinuously extend between the upper surface 104 u of thephotosensitive material 104 and a lower surface 1041 of thephotosensitive material 104. For example, the plurality of depths offocus 112 a-112 b may be contiguous along a vertical direction that isnormal to an upper surface of the photosensitive material 104.Alternatively, the plurality of depths of focus 112 a-112 b may overlapone another along the vertical direction.

Dynamically focusing the electromagnetic radiation 108 over theplurality of different image planes 110 a-110 b spreads theelectromagnetic radiation 108 over a cumulative depth of focus 114 thatis larger than the individual different depths of focus 112 a-112 brespectively associated with the different image planes 110 a-110 b.Since a depth of focus defines a location within which a projected imagehas acceptable optical properties (e.g., focus, dose, etc.) to exposethe photosensitive material 104, the cumulative depth of focus 114provides the photolithography tool 116 with a larger process window. Forexample, in some embodiments the process window of the photolithographytool 116 may be increased by over 30% with respect to fixed depths offocus (e.g., the cumulative depth of focus of the electromagneticradiation 108 may increase from approximately 0.2 um to approximately0.3 um). Furthermore, by using a dynamic exposure method, a lifetime ofthe photolithography tool 116 can be prolong since the dynamic exposurecan compensate for decay of optical elements (e.g., lenses and/ormirrors) with an optical train of the photolithography tool 116.

FIG. 2 illustrates a flow diagram of some embodiments of a method 200 ofdynamically exposing a photosensitive material over a plurality ofdepths of focus respectively spanning a different region of thephotosensitive material.

While method 200 is illustrated and described below as a series of actsor events, it will be appreciated that the illustrated ordering of suchacts or events are not to be interpreted in a limiting sense. Forexample, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the description herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

At 202, a photosensitive material is formed over a substrate. In someembodiments, the photosensitive material may comprise a positive ornegative photoresist. FIG. 3 illustrates some embodiments of across-sectional view 300 corresponding to act 202.

At 204, a pattern within the photosensitive material is exposed toelectromagnetic radiation while changing a focus of the electromagneticradiation. Exposing the photosensitive material to electromagneticradiation modifies a solubility of an exposed region to define a solubleregion within the photosensitive material. In some embodiments, act 204may be performed according to acts 206-208.

At 206, the electromagnetic radiation is focused on a first image planelocated at a first depth below an upper surface of the photosensitivematerial. The first image plane has a first depth of focus spanning afirst region within the photosensitive material.

At 208, the electromagnetic radiation is focused on a second image planelocated at a second depth below the upper surface of the photosensitivematerial. The second image plane has a second depth of focus spanning asecond region within the photosensitive material.

Changing the focus of the electromagnetic radiation changes a locationof an image plane of the electromagnetic radiation and therefore alsochanges a location of a depth of focus of the electromagnetic radiation.Changing the depth of focus of the electromagnetic radiation results inthe electromagnetic radiation being provided over a plurality of depthsof focus respectively spanning a different region of the photosensitivematerial. The changes in focus are generally performed in-situ (i.e.,without breaking a vacuum of a processing chamber in which the exposureprocess is performed). FIGS. 4A-4D illustrate some embodiments ofcross-sectional views corresponding to act 204.

At 210, the photosensitive material is developed to remove the solubleregion and to define an opening within the photosensitive material. FIG.5 illustrates some embodiments of a cross-sectional view 500corresponding to act 210.

At 212, the substrate underlying the opening may be processed, in someembodiments. FIG. 6 illustrates some embodiments of a cross-sectionalview 600 corresponding to act 212.

At 214, the photosensitive material is removed from over the substrate.

It will be appreciated that the method 200 may be performed iterativelyto form successive layers of photosensitive material over a substrate.The successive layers of photosensitive material may comprise differentpatterns. For example, in some embodiments, after a first layer ofphotosensitive material is removed (e.g., according act 214), a secondlayer of photosensitive material may be formed over the substrate (e.g.,according to act 202). A second pattern may be exposed within the secondlayer of photosensitive material while changing a focus of theelectromagnetic radiation, thereby exposing the second layer ofphotosensitive material to electromagnetic radiation at a plurality ofdifferent depths of focus that respectively span a different regionwithin the second layer of photosensitive material (e.g., according toact 204). The second layer of photosensitive material may besubsequently developed to define an opening within the second layer ofphotosensitive material (e.g., according to act 210).

FIGS. 3-6 illustrate cross-sectional views of some embodiments of adynamic lithographic exposure method that exposes a photosensitivematerial over a plurality of depths of focus.

As shown in cross-sectional view 300 of FIG. 3 , a photosensitivematerial 302 is formed over a substrate 102. In various embodiments, thesubstrate 102 may comprise any type of semiconductor body (e.g.,silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductor wafer or oneor more die on a wafer, as well as any other type epitaxial layers,dielectric layers, and/or metal interconnect layers formed thereonand/or otherwise associated therewith. The photosensitive material 302is a material having chemical properties that change when exposed toelectromagnetic radiation (e.g., molecular chains of a photosensitivematerial may become cross-linked when exposed to electromagneticradiation). In various embodiments, the photosensitive material 302 maycomprise a photosensitive polymer such as a positive or negativephotoresist.

In some embodiments, the photosensitive material 302 may be formed ontothe substrate 102 by a spin coating process. The spin coating processdeposits the photosensitive material 302 onto the substrate 102 as aliquid and then subsequently spins the substrate 102 at a high rate ofRPMs (e.g., between 1,000 and 10,000 RPM) to give the layer ofphotosensitive material 302 a uniform thickness. In other embodiments,the photosensitive material 302 may be formed onto the substrate 102 byother processes (e.g., by vapor deposition processes).

FIGS. 4A-4D illustrate cross-sectional views showing a dynamic exposureof the photosensitive material 302 to electromagnetic radiation over aplurality of depths of focus. The dynamic exposure of the photosensitivematerial 302 causes segments of photosensitive material 302 to achievedifferent solubilities to a chemical developer. Although FIGS. 4A-4Dillustrates an embodiments wherein an exposed region of thephotosensitive material 302 becomes soluble (e.g., as with a positivephotoresist), it will be appreciated that the disclosure is not limitedto such embodiments. Rather, in other embodiments the exposed region ofthe photosensitve material 302 may become insoluble while unexposedregions of the photosensitve material 302 may remain soluble (e.g., aswith a negative photoresist).

As shown in cross-sectional view 400 of FIG. 4A, at a first time (t=1) aphotomask 118 is aligned with the substrate 102. In some embodiments,alignment may be performed by moving a wafer stage 402 (e.g., a vacuumwafer chuck) holding the substrate 102 to align alignment marks on thephotomask 118 with alignment marks on and/or within the substrate 102.

As shown in cross-sectional view 404 of FIG. 4B, once alignment iscompleted electromagnetic radiation from a photolithography tool 116 isselectively provided to the photosensitive material 302 according to apattern defined by the photomask 118. At a second time (t=2), theelectromagnetic radiation is focused along a first set of paths 406 athat converge along a first image plane 408 a. In some embodiments, thefirst image plane 408 a may be located at a first depth d₁ below anupper surface of the photosensitive material 302. In other embodiments,the first image plane 408 a may be located at or above the upper surfaceof the photosensitive material 302. The first image plane 408 a providesthe electromagnetic radiation with a first depth of focus 410 a spanninga first region within the photosensitive material 302.

As shown in cross-sectional view 412 of FIG. 4C, a focus of theelectromagnetic radiation is changed at a third time (t=3). The changein focus causes the electromagnetic radiation to be selectively providedto the photosensitive material 302 (according to the pattern defined bythe photomask 118) along a second set of paths 406 b that converge alonga second image plane 408 b. The second image plane 408 b is located at asecond depth d₂ below the upper surface of the photosensitive material302, wherein the second depth d₂ is greater than the first depth d₁. Thesecond image plane 408 b provides the electromagnetic radiation with asecond depth of focus 410 b spanning a second region within thephotosensitive material 302. In various embodiments, the first depth offocus 410 a may be contiguous with or overlap the second depth of focus410 b. In some embodiments, because the electromagnetic radiation isfocused on a same pattern during the second time (t=2) and the thirdtime (t=3), no alignment is performed between the second time (t=2) andthe third time (t=3).

As shown in cross-sectional view 414 of FIG. 4D, a focus of theelectromagnetic radiation is changed at a fourth time (t=4). The changein focus causes the electromagnetic radiation to be selectively providedto the photosensitive material 302 (according to the pattern defined bythe photomask 118) along a third set of paths 406 c that converge alonga third image plane 408 c. The third image plane 408 c is located at athird depth d₃ below the upper surface of the photosensitive material302, wherein the third depth d₃ is greater than the second depth d₂. Invarious embodiments, the third image plane 408 c may be within thephotosensitive material 302 or below a lower surface of thephotosensitive material 302. The third image plane 408 c provides theelectromagnetic radiation with a third depth of focus 410 c spanning athird region within the layer of photosensitive material 302. In someembodiments, the third depth of focus 410 c may be contiguous with oroverlap the second depth of focus 410 b.

The exposure of the photosensitive material 302 to the electromagneticradiation changes chemical properties of the photosensitive material 302within an exposed region 418. The change in chemical properties resultsin the exposed region 418 having a different solubility than unexposedregions 416 of the photosensitive material. In some embodiments, thephotosensitive material 302 may be continuously exposed to theelectromagnetic radiation according to the pattern defined by thephotomask 118 while dynamically changing a depth of focus of theelectromagnetic radiation. In other embodiments, the photosensitivematerial 302 may be discretely exposed to the electromagnetic radiationaccording to the pattern defined by the photomask 118 while changing adepth of focus of the electromagnetic radiation (e.g., thephotosensitive material 302 may be exposed to discrete bursts ofelectromagnetic radiation between changing a depth of focus of theelectromagnetic radiation).

As shown in cross-sectional view 500 of FIG. 5 , the photosensitivematerial 506 is developed to remove a soluble region and define anopening 502 within the photosensitive material 506. The photosensitivematerial 506 may be developed by exposing the photosensitive material506 to a chemical developer 504. In some embodiments, the chemicaldeveloper 504 removes the exposed region (418 of FIG. 4D) of thephotosensitive material, while the unexposed regions (416 of FIG. 4D)remain over the substrate 102. In other embodiments, the chemicaldeveloper 504 may remove unexposed regions (416 of FIG. 4D) of thephotosensitive material, while the exposed region (418 of FIG. 4D)remains over the substrate 102. In some embodiments, the chemicaldeveloper 504 may comprise tetramethylammonium hydroxide (TMAH). Inother embodiments, the chemical developer 504 may comprise potassiumhydroxide (KOH), sodium hydroxide (NaOH), acetate, ethyl lactate, ordiacetone alcohol, for example.

As shown in cross-sectional view 600, the substrate 602 is processedaccording to the patterned photosensitive material 506. In someembodiments, the substrate 602 may be selectively etched by exposing thesubstrate 602 to an etchant 604 according to the patternedphotosensitive material 506. For example, in some embodiments, thesubstrate 602 may comprise a dielectric layer, overlying a semiconductorbody, which is exposed to the etchant 604 to form a via hole or a metaltrench used to form a metal interconnect layer of an integrated chip. Inother embodiments, the substrate 602 may be selectively implanted byimplanting the substrate 602 with a dopant species according to thepatterned photosensitive material 506.

The patterned photosensitive material 506 may be subsequently removed(i.e., stripped) after the processing of the substrate 602 has beenperformed. In some embodiments, the patterned photosensitive material506 may be removed by a dry etching process.

FIG. 7A illustrates a block diagram of some embodiments of a dynamiclithographic exposure tool 700 configured to expose a photosensitivematerial over a plurality of depths of focus.

The dynamic lithographic exposure tool 700 comprises an illuminationsource 702 configured to generate electromagnetic radiation. In someembodiments, the illumination source 702 may be configured to generateelectromagnetic radiation within the deep ultraviolet region of theelectromagnetic spectrum (e.g., approximately 193 nm). In suchembodiments, the illumination source 702 may comprise an excimer laser(e.g., comprising a krypton fluoride laser at approximately 248 nmwavelength or an argon fluoride laser at approximately 193 nmwavelength), for example. In other embodiments, the illumination source702 may be configured to generate electromagnetic radiation within theextreme ultraviolet (EUV) region of the electromagnetic spectrum (e.g.,approximately 13.5 nm). In yet other embodiments, the illuminationsource 702 may be configured to generate electromagnetic radiation inother regions of the electromagnetic spectrum (e.g., radiation havingwavelengths of approximately 248 nm, approximately 365 nm, and/orapproximately 405 nm).

The electromagnetic radiation generated by the illumination source 702is provided to condensing optics 704 configured to focus theelectromagnetic radiation. In various embodiments, the condensing optics704 may comprise a first plurality of optical elements, such as lenses,mirrors, filters, etc. The focused radiation is provided from thecondensing optics 704 to a photomask 706 configured to selectivelytransmit electromagnetic radiation to projection optics 708 according tofeatures on the photomask 706. In some embodiments, the photomask 706may comprise an opaque material arranged over a transparent substrate(e.g., chrome arranged over a glass substrate). In other embodiments,the photomask 706 may comprise a phase shift mask comprising a phaseshifting layer (e.g., molybdenum silicon oxy-nitride(Mo_(x)Si_(y)ON_(z))) arranged between opaque shielding layer (e.g.,chrome) and a transparent substrate. In yet other embodiments, thephotomask 706 may comprise an extreme ultraviolet (EUV) mask comprisinga patterned absorber arranged over a multi-layer reflective coatingdisposed on a low thermal expansion material.

The projection optics 708 are configured to focus the electromagneticradiation 710 along paths that converge along an image plane 712 toproject a pattern (defined by features of the photomask 706) within aphotosensitive material 302 overlying a substrate 102 held by a waferstage 716. The image plane 712 has a depth of focus 714 within which theoptical properties (e.g., focus, dose, etc.) of the electromagneticradiation are sufficient to expose the photosensitive material 302 andto form soluble regions within the photosensitive material 302 accordingto an accepted yield criteria (e.g., the electromagnetic radiation hasoptical properties that provide for a yield of greater than 90%). Invarious embodiments, the projection optics 708 may comprise a secondplurality of optical elements, such as lenses, mirrors, filters, etc.

A dynamic focal element 718 is configured to vary a location at whichthe projection optics 708 are focused during exposure of the patternwithin the photosensitive material 302. Varying a location at which theprojection optics 708 are focused changes a position of the image plane712 of the projection optics 708. By changing the position of the imageplane 712 of the projection optics 708, the photosensitive material 302is exposed to electromagnetic radiation at multiple depths of focus thatrespectively span a different region within the photosensitive material302. By exposing the pattern at multiple depths of focus,electromagnetic radiation 710 having acceptable optical propertiesprovided to a cumulative depth of focus that is larger than a depth offocus of a stationary image plane, thereby improving a process window ofthe dynamic lithographic exposure tool 700.

FIG. 7B illustrates some embodiments of a diagram 720 showing exemplarydoses for different depths of focus achieved by the disclosed dynamiclithographic exposure tool 700.

As shown in diagram 720, during a first time (t=1) electromagneticradiation is focused at a first image plane that provides for a firstdepth of focus 722 spanning a first range of spatial positions. Withinthe first depth of focus 722, the electromagnetic radiation has avarying dose. For example, within a center of the first depth of focus722 (F_(cen1)), the electromagnetic radiation has a largest dose.However, as the distance from the center of the first depth of focus 722increases, the dose of the electromagnetic radiation decreases (e.g.,the dose at F_(cen1)+Δf and F_(cen1)−Δf is smaller than the dose atF_(cen1)).

During a second time (t=2) electromagnetic radiation is focused at asecond image plane that provides for a second depth of focus 724spanning a second range of spatial positions different than the firstrange of spatial positions. Within the second depth of focus 724, theelectromagnetic radiation also has a varying dose. For example, within acenter of the second depth of focus 724 (F_(cen2)), the electromagneticradiation has a largest dose. However, as the distance from the centerof the second depth of focus 724 increases, the dose of theelectromagnetic radiation decreases (e.g., the dose at F_(cen2)+Δf andF_(cen2)−Δf is smaller than the dose at F_(cen2)).

The cumulative effect of the exposures during the first time (t=1) andthe second time (t=2) results in a cumulative depth of focus 726 thatprovides for improved dose over a larger range of spatial positions. Forexample, while the electromagnetic radiation at each of the first time(t=1) and the second time (t=2) have depths of focus that extendsbetween F_(cen)+Δf and F_(cen)+Δf, the cumulative depth of focus extendsbetween F_(cen)+2Δf and F_(cen)−2Δf (wherein Δf is a incremental changein focus). Therefore, the dynamic lithographic exposure tool 700increases the process window from 2Δf to 4Δf.

FIG. 8 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool 800.

The dynamic lithographic exposure tool 800 comprises a database 804 thatis in communication with a dynamic focal element 802. The database 804may be configured to store information relating to a substrate 102and/or photosensitive material 302 to be processed, and to provide theinformation S to the dynamic focal element 802. In various embodiments,the database 804 may store a thickness of the substrate 102, a thicknessof a photosensitive material 302 overlying the substrate 102, a minimumfeature size to be resolved in the photosensitive material 302, aresolution required to achieve the minimum feature size, a type ofphotoresist material being used, a distance (d) between the projectionoptics 708 and a wafer stage 808 configured to hold the substrate 102(e.g., a vacuum wafer chuck), etc. In some embodiments, the informationstored within the database 804 may be determined based upon informationfrom other process tools. For example, the database 804 may receive athickness of the photosensitive material 302 from a spin coating tool(e.g., based upon a type of photoresist used and one or more speeds usedto apply the photoresist onto the substrate 102).

Based upon the information S provided by the database 804, the dynamicfocal element 802 is able to determine operational parameters of thedynamic lithographic exposure tool 800. For example, in someembodiments, the dynamic focal element 208 may determine a range overwhich a focus (e.g., a location of an image plane, a location of a depthof focus, etc.) of the projection optics 708 is to be varied duringexposure of the photosensitive material 302 based upon a thickness ofthe photosensitive material 302 received from the database 804. In otherembodiments, the dynamic focal element 208 may determine a rate ofchange of the focus of the projection optics 708 based upon a type ofphotosensitive material 302 or desired dose received from the database804 (so as to provide for a proper dose to the photosensitive material302). In yet other embodiments, the dynamic focal element 802 maydetermine a location of an initial image plane of the projection optics708 (e.g., based upon a thickness of the photosensitive material 302 andthe distance (d) between the projection optics 708 and the wafer stage808 received from the database 804).

The dynamic focal element 802 is subsequently configured to generate acontrol signal S_(CTRL) based upon the operational parameters. Thecontrol signal S_(CTRL) operates the projection optics 708 and/or awafer stage 716 to dynamically vary a focus of the projection optics 708during exposure of a pattern within the photosensitive material 302,thereby projecting electromagnetic radiation along a plurality ofdifferent paths 806 a-806 c at different times. The plurality ofdifferent paths 806 a-806 c respectively correspond to image planeshaving different depths of focus respectively spanning a differentregion of the photosensitive material 302.

FIG. 9 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool 900.

The dynamic lithographic exposure tool 900 comprises a dynamic focalelement 906 having an actuator 908 and a control unit 910. The controlunit 910 is configured to operate the actuator 908 to change a locationof one or more elements of the dynamic lithographic exposure tool 900 toexpose a photosensitive material 302 over a substrate 102 at a pluralityof depths of focus respectively spanning a different region of thephotosensitive material. In some embodiments, the dynamic focal element906 may be in further communication with a database 804 configured toprovide information to the dynamic focal element 906.

In some embodiments, the actuator 908 may be configured to dynamicallymove a location of a wafer stage 716 holding the substrate 102 duringexposure of a photosensitive material 302 over a substrate 102. In suchembodiments, the actuator 908 may move the wafer stage 716 along adirection 912 during exposure of the photosensitive material 302. Bymoving the wafer stage 716 along the direction 912, the image plane 914(i.e., the plane in which the image of the photomask 706 is projected)and a corresponding depth of focus changes.

In other embodiments, the dynamic lithographic exposure tool 900 maycomprise projection optics 902 having an ambulatory projection element904 configured to focus electromagnetic radiation from photomask 706onto the photosensitive material 302. In various embodiments, theambulatory projection element 904 may comprise a lens and/or a mirror.In such embodiments, the dynamic focal element 906 is in communicationwith the ambulatory projection element 904. The dynamic focal element906 is configured to change a location of the ambulatory projectionelement 904 (along direction 912) so as to change a distance between theambulatory projection element 904 and an object to be projected onto thephotosensitive material 302. Changing the location of the ambulatoryprojection element 904 changes the focus of the projection optics 902.

In some embodiments, the control unit 910 may be configured to operatethe actuator 908 to change the location of the ambulatory projectionelement 904 during exposure of a pattern within the photosensitivematerial 302. By changing the location of the ambulatory projectionelement 904, the image plane 914 (i.e., the plane in which the image ofthe photomask 706 is projected) and a corresponding depth of focuschanges. For example, according to the thin lens equation(1/f=1/d_(i)+1/d_(o)) the distance d_(i) at which the object plane isformed is equal to d_(i)=(f*d_(o))/(d_(o)−f). Since the focal length fof an optical component (e.g., a lens) is a constant, the distance d_(i)at which the image plane 914 is formed can be changed by changing adistance d_(o) between the object (e.g., the photomask 706 or an imagegenerated from the photomask 706) and the ambulatory projection element904.

Although the dynamic lithographic exposure tool 900 illustrates theprojection optics 902 as comprising a single ambulatory projectionelement 904, it will be appreciated that the projection optics 902 maycomprise multiple optical elements (e.g., lens, mirrors, filters, etc.).Furthermore, while the dynamic lithographic exposure tool 900 isillustrated as changing the depth of focus by varying a location of theambulatory projection element 904 it will be appreciated that this isnot a limiting means of changing the depth of focus and that inalternative embodiments the depth of focus may be changed in alternativeways (e.g., by changing a numerical aperture of the projection optics902).

FIG. 10 illustrates a block diagram of some embodiments of a dynamiclithographic exposure tool 1000 for an extreme ultraviolet (EUV)lithography system.

The dynamic lithographic exposure tool 1000 comprises an EUV radiationsource 1002 configured to emit extreme ultraviolet (EUV) radiation 1004a (e.g., having wavelengths in a range of about 10 nm to about 130 nm).The emitted EUV radiation 1004 a is supplied as to an EUV photomask 1006configured to selectively reflect the EUV radiation 1004 a, as reflectedEUV radiation 1004 b. The reflected EUV radiation 1004 b is provided toprojection optics 708 configured to focus the reflected EUV radiation1004 b in a manner that selective patterns a photosensitive material 302disposed over a substrate 102. A dynamic focal element 802 is configuredto operate the projection optics 708 to vary a depth of focus of thereflected EUV radiation 1004 b during exposure of a pattern on thephotosensitive material 302.

In some embodiments, the EUV photomask 1006 comprises a pellicle 1016mounted on an EUV reticle 1008. The pellicle 1016 comprises a thin filmthat is configured to prevent contaminant particles from landing on theEUV reticle 1008 and degrading performance of the dynamic lithographicexposure tool 1000. The EUV reticle 1008 comprises a reflectivemulti-layer reflective coating disposed over a low thermal expansionmaterial (LTEM) 1009. The multi-layer reflective coating comprisesplurality of reflective layers 1010 separated by a plurality of spacerlayers 1012. A patterned absorber material 1014 configured to absorb(i.e., attenuate) the EUV radiation 1004 a is disposed over themulti-layer reflective coating. In some embodiments, a buffer layer (notshown) may be disposed between the multi-layer reflective coating andthe patterned absorber material 1014. The buffer layer is configured toact as a capping layer to prevent oxidation of a top one of thereflective layers 1010 by exposure to an ambient environment.

In some embodiments, the reflective layers 1010 may comprise molybdenum(Mo) or ruthenium (Ru) and the spacer layers 1012 may comprise silicon(Si). The reflective layers 1010 are configured to reflect the EUVradiation 1004 a by means of Bragg interference between multi-interlayerinterference formed between the reflective and spacer layers, 1010 and1012, respectively. For example, the EUV radiation 1004 a may bepartially reflected at a first interlayer interface formed between afirst reflective layer and a first spacer layer and partially reflectedat a second interlayer interface formed between a second reflectivelayer and a second spacer layer.

FIG. 11 illustrates a block diagram of some additional embodiments of adynamic lithographic exposure tool 1100 for an EUV lithography system.Although the dynamic lithographic exposure tool 1100 is illustrated ashaving a certain configuration of components, it will be appreciatedthat the disclosed EUV radiation source may be implemented in EUVphotolithography systems having additional components (e.g., additionalmirrors) or having less components (e.g., less mirrors).

The dynamic lithographic exposure tool 1100 comprises an EUV radiationsource 1002 configured to supply EUV radiation 1114 (i.e., with awavelength of between approximately 10 nm and approximately 130 nm) toan EUV photomask 1006 having a patterned multi-layered reflectivesurface. In some embodiments, the EUV radiation source 1002 may comprisea primary laser 1102, a fuel droplet generator 1106, and a collectormirror 1112. The fuel droplet generator 1106 is configured to providefuel droplets 1108, which are hit with a primary laser beam 1104generated by the primary laser 1102. Striking the fuel droplets 1108with the primary laser beam 1104 generates a plasma 1110 comprising ionsthat emit EUV radiation 1114 at a wavelength of between approximately 10nm and approximately 130 nm (e.g., at a wavelength of 13.5 nm).

The EUV radiation 1114 output from the EUV radiation source 1002 isprovided to a condensing optics 1120 by way of an intermediate focusunit 1116. In some embodiments, the condensing optics 1120 comprisefirst and second surfaces, 1122 a and 1122 b, configured to focus theEUV radiation 1114, and a reflector 1124 configured to reflect the EUVradiation 1126 towards the EUV photomask 1006. The EUV photomask 1006 isconfigured to selectively reflect the EUV radiation 1128 to projectionoptics 1130 that project a pattern onto a layer of photosensitivematerial (e.g., photoresist) disposed over the semiconductor workpiece1132. To produce the pattern, the EUV photomask 1006 comprises apatterned absorber material arranged on a front surface of the EUVphotomask 1006. The patterned absorber material is configured to absorbthe EUV radiation 1126, such that the reflected rays of EUV radiation1128 convey a pattern defined by the EUV photomask 1006.

In some embodiments, the projection optics 1130 may comprise a series ofmirrors 1130 a-1130 d, which serve to reduce a size of the patterncarried by the EUV radiation 1128. The series of mirrors 1130 a-1130 dconvey the EUV radiation 1128 onto the layer of photosensitive material(e.g., photoresist) disposed over the semiconductor workpiece 1132. Adynamic focal element 802 is configured operate upon the projectionoptics 1130 to vary a depth of focus of the EUV radiation 1128 projectedonto the layer of photosensitive material. In some embodiments, thedynamic focal element 802 may be configured to dynamically varylocations of one or more of the mirrors 1130 a-1130 d. The EUV radiation1128 patterns the layer of photosensitive material so that subsequentprocessing can be performed on selected regions of the semiconductorworkpiece 1132.

Therefore, the present disclosure relates to a dynamic lithographicexposure method, and an associated apparatus, which changes a focus ofelectromagnetic radiation during exposure of a photosensitive materialto cause the electromagnetic radiation to have a plurality of differentdepths of focus that respectively span a different region of thephotosensitive material. The different depths of focus provide for acumulative depth of focus that is larger than the individual differentdepths of focus, and therefore results in a larger lithographic processwindow that improves exposure of the photosensitive material.

In some embodiments, the present disclosure relates to a method ofdeveloping a photosensitive material. The method comprises forming aphotosensitive material over a substrate. The method further comprisesexposing the photosensitive material to electromagnetic radiation at aplurality of depths of focus that respectively span a different regionwithin the photosensitive material. Exposing the photosensitive materialto the electromagnetic radiation modifies a solubility of an exposedregion within the photosensitive material. The method further comprisesdeveloping the photosensitive material to remove the soluble region.

In other embodiments, the present disclosure relates to a method ofdeveloping a photosensitive material. The method comprises forming aphotosensitive material over a substrate. The method further comprisesfocusing electromagnetic radiation on a first image plane at a firsttime. The first image plane is located at a first depth below an uppersurface of the photosensitive material. The method further comprisesfocusing the electromagnetic radiation on a second image plane at asecond time. The second image plane is located at a second depth belowthe upper surface of the photosensitive material. Exposing thephotosensitive material to the electromagnetic radiation modifies asolubility of an exposed region of the photosensitive material.

In yet other embodiments, the present disclosure relates to aphotolithography tool. The photolithography tool comprises anillumination source configured to generate electromagnetic radiation.Projection optics are configured to focus the electromagnetic radiationonto a photosensitive material overlying a substrate according to apattern on a photomask. A dynamic focal element is configured todynamically change a focus of the projection optics during exposure ofthe photosensitive material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A photolithography tool, comprising: a sourceconfigured to generate electromagnetic radiation; a dynamic focal systemconfigured to provide the electromagnetic radiation to a plurality ofdifferent vertical positions over a substrate stage; and wherein theplurality of different vertical positions comprise a first positionhaving a first depth of focus and a second position having a seconddepth of focus that is below the first depth of focus and thatvertically overlaps the first depth of focus.
 2. The photolithographytool of claim 1, wherein the substrate stage is configured to hold asubstrate, the first position and the second position configured to bewithin a photosensitive material over the substrate.
 3. Thephotolithography tool of claim 2, wherein the first depth of focus andthe second depth of focus both expose a same pattern in thephotosensitive material.
 4. The photolithography tool of claim 1,further comprising: projection optics disposed between a photomask andthe substrate stage, wherein the dynamic focal system is configured tooperate on the projection optics to provide the electromagneticradiation to the plurality of different vertical positions.
 5. Thephotolithography tool of claim 4, wherein the photomask comprises apellicle mounted on an extreme ultraviolet (EUV) reticle.
 6. Thephotolithography tool of claim 4, wherein the projection optics comprisea plurality of mirrors.
 7. The photolithography tool of claim 1, whereina first maximum dose of the electromagnetic radiation within the firstdepth of focus is vertically separated from a second maximum dose of theelectromagnetic radiation within the second depth of focus.
 8. Thephotolithography tool of claim 1, wherein the electromagnetic within thefirst depth of focus has a first dose that is above a first value over afirst spatial region spanning a first depth and the electromagneticradiation within the second depth of focus has a second dose that isabove the first value over a second spatial region spanning a seconddepth; and wherein a collective dose of the electromagnetic radiation,received over both the first depth of focus and the second depth offocus, is above the first value over a third spatial region spanning athird depth that is larger than the first depth or the second depth. 9.The photolithography tool of claim 1, wherein the first position isdirectly above or below the second position.
 10. A photolithographytool, comprising: a source configured to generate electromagneticradiation; a dynamic focal system configured to focus theelectromagnetic radiation over a first depth of focus at a first timeand to focus the electromagnetic radiation over a second depth of focusat a second time, wherein the first depth of focus has a largest dose ata first position and the second depth of focus has a largest dose at asecond position; and wherein the first depth of focus and the seconddepth of focus collectively provide a highest dose within an area ofoverlap between the first depth of focus and the second depth of focus.11. The photolithography tool of claim 10, further comprising: asubstrate stage configured to hold a substrate, wherein the firstposition and the second position are configured to be within aphotoresist material over the substrate.
 12. The photolithography toolof claim 10, wherein the source is configured to generate theelectromagnetic radiation to have a wavelength of approximately 13.5 nm.13. The photolithography tool of claim 10, wherein the dynamic focalsystem comprises: an actuator in communication with one or more opticalelements configured to act upon the electromagnetic radiation; and acontrol unit configured to control operation of the actuator.
 14. Thephotolithography tool of claim 10, wherein the first depth of focus andthe second depth of focus collectively define a cumulative depth offocus that has a first process window that is over 30% larger than asecond process window provided by either the first depth of focus or thesecond depth of focus.
 15. A photolithography tool, comprising: a sourceconfigured to generate electromagnetic radiation; a dynamic focal systemconfigured to focus the electromagnetic radiation at a first depth offocus at a first time and to focus the electromagnetic radiation at asecond depth of focus at a second time, the first depth of focusvertically offset from the second depth of focus; and wherein aphotosensitive material that is over a substrate is configured toreceive the electromagnetic radiation at both the first time and at thesecond time.
 16. The photolithography tool of claim 15, wherein theelectromagnetic radiation exposes the photosensitive material to a samepattern at both the first depth of focus and the second depth of focus.17. The photolithography tool of claim 15, wherein the first depth offocus and the second depth of focus are respectively smaller than athickness of the photosensitive material.
 18. The photolithography toolof claim 15, wherein the photosensitive material is exposed to separatebursts of electromagnetic radiation at the first time and at the secondtime.
 19. The photolithography tool of claim 15, wherein the first depthof focus and the second depth of focus collectively define a cumulativedepth of focus that has a first process window that is larger than asecond process window provided by either the first depth of focus or thesecond depth of focus.
 20. The photolithography tool of claim 15,further comprising: a control unit configured to control an actuatorthat changes the dynamic focal system between the first depth of focusand the second depth of focus.